Resistance device and method of making same



' Sept. 4, 1928.

/ 1,683,060 c. E. VAWTER RESISTANCE DEVICE AND METHOD OF MAKING SAIIEFil 6d Sept. 18, 1924 INVENTOR MARLES E. 1VAWTR ATTORNEY Patented Sept.4, 1928.

UNITED STATES PATENT OFFICE.

CHARLES E. VAWTER, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR '.!.ODUBILIER CONDENSER CORPORATION, OF NEW YORK, N. Y., A CORPORATION OFDELAWARE.

RESISTANCE DEVICE AND METHOD OF MAKING SAME.

Application filed September 18, 1924. Serial No. 738,422.

My invention relates to electrical resistance devices of the typedisclosed in my ranging from a few thousand ohms to several megohms arerequired. These res1stances should have relativelyhigh currentcarryincapacity, and should not change materia y with a rise or fall intemperature.

In other words, the resistances should be substantially constant. It isdesirable to provide a simple and easily manufactured resistancedevice-of this nature, capable of presenting and maintaining aresistance having the required and predetermined value;

also to originate a method by which such devices can be readily andinexpensively produced. The present invention has been made with a viewto obtaining these results.

I have found that a very satisfactory resistance device can be made byinserting a quantity of suitable material, preferably in the form of apaste, into an insulating casing, and then subjecting the device to furwther treatment. Preferably the casing should be porous, to enable it andits contents to bedthoroughly dried and then coated and scale i Thenature of my invention will be aps5 parent from the followin detaileddescription, which is to be considered in conjunction with theaccompanying drawings, in which: Figure 1 is a longitudinal elevation,partly in section, of the completed resistance device according to myinvention.

The same numerals. identify the same parts throughout.

The numeral 1 on the drawing indicates L5 a tube or spool of somesuitable porous insulating material such as wood. This tube may have itsends bored out larger for a purpose to be explained later. The ends ofthe tube are closed by caps 2 of some conductive s0 material such asmetal, and the inside of the tube is filled with :1. treated resistancematerial 3. Each cap 2 has a projection 4.- which can be thrust into theadjacent enlarged end of the bore of the tube, this proi 5 jection 4being in the form of a shank or mixture of manganese dioxide, lamp-blackboss having threads 5 or being otherwise roughened on its exteriorsurface.

The resistance material 3 contains a binder which is of such a naturethat it not only causes the material 3 to cohere, but also makes itadhere tightly to the metal proections 4 of cap '2, which the material 3completely surrounds; and to the inside of the tube 1. I

Hence the caps are firmly cemented to the ends of the tube and efficientand permanent electrical contact between the cap and the resistancematerial 3 is obtained.

The material 3 consists preferably of a and glue. The manganese dioxideis ground to powder and mixed with lamp-black in approximately equalproportions. Le Page liquid glue can then be added, the entire massbeing agitated in a stirring vessel to intermix the ingredientsthoroughly; while the operation of filling a number of tubes like thetube 1 is performed. After mixing the manganese dioxide and lamp-blackin equal'proportions, the glue can be added in such quantity that, forexample, for every twenty parts by weight of the manganese dioxide andlamp-black 125145 parts of glue will be present. When the mixture hasbeen made, it is utilized to fill a selected number of tubes or spools1, by means of a squirt gun or any other apparatus. As each tube orcasing lis filled up to both ends, the caps 2 are puton immediately andin this condition, then tube is air dried for about one week.-

While drying, the filled tubes with their caps in place are put insuitable holders to prevent the caps from working off the ends of tubeswhile the caps are becoming set in the process ofdrying. After dryingfor about seven days they are heated at 125 to 150 for 2 to 3 hours, andthen placed in a paraflin bath under a vacuum for some minutes to removeall air and all traces of 1 remaining moisture. Then air is againadmitted under any desired pressure until all interior spaces arethoroughly filled with: paraffin.

Next each of the devices are treated elec- 105 trically by testing at800 volts and then allowed to lie one week for aging. The resistancedevices are-now segregated and classified according to the differentvalues of the resistance which they present, by measure- 110 ment, forexample, at 220 volts, and then sired with a given mixture, 'the middlesecafter another week these measurements can be checked at a lowervoltage, such as six volts. This precaution is taken to detect anychanges in the value of the resistance which may have taken place. Allof the devices which are satisfactory are then taken and labeled andpacked, the other ones which are not satisfactory can be treated furtherin the same way until they attain the condition required.

When finished, the resistance devices having the structure and characterabove indi' cated are perfectly dried and entirely mois ture-proof.Their resistance is constant and will not chan e in service, and eachdevice will have su cient mechanical strength to enable it to withstandhandling and avoid damage when subjected to the ordinary carelessmanipulation frequently given to appliances of this sort.

By the method above described, I can make resistance devices from 1200to 100,000 ohms or in higher resistance values from 100,000 to20'megohms. The devices are particularly useful as grid leaks for radiosets and their resistance remains constant. They are not subject to thegradual increase of resistance values so marked in most types ofhighresistances, usually due to poorcontact between resistance materialand metal ends. The resistance of the manganese dioxide is always high;while that of the carbon which is referably in the form of lamp-black isreliitively low and by intermixing these with the adhesive or glue andtreating as described, the finished device is given the value ofresistance which is required and this resistance is maintained.

The end caps 2 do not fit the exterior of the tube 1 tightly, but have aslight clearance (about 1/100 of an inch) to enable resistance material3 after being inserted in the tube 1' to escape when caps 2 are pushedon; and at the same time give better electrical contact. The resistancematerial after drying becomes stony yet somewhat resilient, likehardened glue.

Glue is used advisedly rather than shellac, l uer, etc., as-it'has abetter conductivity.

e attainment of good and lasting electrical contact by the adhesion ofthe resistance material 3 to the metal caps 2 is an important feature ofthis invention.

The same constant resistance can be obtained with different aging eriodsbut I find that the seven day perio s give the desired results andpermit a systematic and eas method to be employed.

he projections require an enlarged recess 6 at each end of the bore ofthe tube 1 of a certain diameter to allows space around the projections4 for the resistance material to cement the projections 4 to the insideof the tube 1. If higher resistances are detion of the tube can be boredout to any required smaller diameter.

Having described my invention, what I believe to be new and desire tosecure and protect by Letters Patent of the United States is 1. Aresistance device comprising a porous insulating casing, electricallyconductive caps on the casing, conductive material in the casingconnecting the caps and capable of presenting a constant resistance to acurrent flowing therethrough, and a coating on said casing, the devicebeing dried and airtight.

2. A resistance device comprising a casing in the form of an open-endedtube of'porous insulating material, electrically conductive capsengaging the ends of said tube, a conductive substance in said tubecomprising manganese dioxide mixed with carbon capable of offering aconstant resistance to the passage of current flowing therethrough, thedevice and contents being thoroughly dried, and thoroughly impregnatedwith a waterproof and insulating material.

3. A resistance device comprising an openended tube of insulatingmaterial filled with an electrically conductive substance, and end capsaflixed to the tube, each of said caps having a roughened projectionwhich extends into the tube and adheres to the resisgance material whichsurrounds it in the tu e.

4. A conductive substance of constant resistance, consisting ofmanganese dioxide and carbon in equal parts by weight, and containinga'binder or adhesive, mingled to aiford a uniform plastic mixture.

5. A conductive substance capable of maintaining a uniform resistance,said substance containing equal parts by weight of manganese dioxide andpowdered carbon mixed with an adhesive in the proportion of twenty partsof the manganese dioxide and carbon to 125 or more parts of theadhesive, mingled to afiord a uniform mixture.

6. The process of manufacturing resistance devices which consists inmaking a mixture of a conductive substancewith an adhesive, forcing saidmixture into a tube, closing the ends of said tube with caps ofelectrically conductive material, subjecting said tube and contents tothe action of heat and then coating the entire device to render itimpervious to moisture and at the same time, extracting all of the airand moisture therefrom.

"7. The process of manufacturing electrical resistance devices whichconsists in making a mixture of manganese dioxide and lampblack with theaddition of an adhesive, forein said mixture into a porous insulating tue, capping the ends of said tube, drying said device, subjecting thedevice to the action of heat and then impregnating the device to make itwater-tight; while at the same time, extracting all of the air andmois-' ture therein, and finally aging the device.

8. The process of manufacturing resistance devices which consists in themaking of.

a mixture of manganese dioxide and lampblack in owdered form, in equalparts by weight, a ding a relatively large quantity of an adhesive andthoroughly intermingling the adhesive with the lamp-black and manganesedioxide, forcing said mixture into'a porous insulating casing, closingthe ends of said casing with electrically conductive caps, subjecting itto the action of heat, and then extracting the air in the casing andcontents, impregnating said device with meltedv wax, to make the sameair-tight and water-proof.

9. A resistance device comprising a cas-' ing, resistance materialcapable of being forced in the form of a paste into'the casing, andterminals on the ends of the casing to be engaged by said material tocause the terminals to adhere to the casin upon the drying of saidmaterial to make e cient electrical contact with said material.

10. A resistance device comprising a casing, plastic resistance materialfilling said casing and terminals on the ends of the cas ing connectedto said material by adhesive enga ment therewith, to cause said terminas to be maintained upon the casing and make eilicient electricalcontacts with said material.

Signed at Philadelphia in the county of Philadelphia and State ofPennsylvania this 29th day of August A. D. 1924.

CHARLES E. VAWTER. I

